The ozone hole has passed maximum development, though central values are still below 120 DU. The vortex has resumed its elliptical shape and the edge of the ozone hole crossed the tip of South America and the Falkland Islands over October 12 to 15. Ozone values over Weddell Sea areas are at minimum and are 60% below normal. Ozone values over the Antarctic Peninsula vary according to the position of the ozone hole but are currently over 50% below normal.


1. Data from the British Antarctic Survey (BAS) Halley station (76-deg south, 26-deg west, on the Brunt ice shelf).

a) Ozone. Total ozone values fell from an estimated 300 DU in early July to around 200 DU in mid August. Values rose to around 240 DU towards the end of August but then steadily fell to 115 DU in early October. The decline has now levelled out. Day to day variation is around 5 DU. Ozone values are comparable to those of the past few years, but well below the long-term mean, with depletion at around 60%. The station is close to the centre of the polar vortex.

Halley preliminary mean daily total ozone, (DU)
Dobson No 103: Instrument constants revised 1997 May 2 and minor revision 1997 September 26 and 1997 October 17.
(0 indicates no data)

194 0 194 195 213 214 221 215 230 217

0 0 0 0 0 0 221 251 210 194 187

179 192 186 186 219 219 208 194 172 183

189 168 170 157 181 179 146 154 167 172

161 155 137 133 128 139 146 131 123 123

154 125 117 121 122 118 113 115 125 114

114 117 128 121 117 120

b) Radiosonde data. Data from Halley show that the mean 100 hPa temperature increased substantially towards the end of August, from close to the long term norm of -83 deg C, to -78 deg C, near the upper limit of the long term range. The temperature then dropped to near normal and has since varied between -84 deg C and -79 deg C in response to planetary waves. It is currently -82 deg C compared to the long term norm of -74 deg C. Stratospheric clouds, which are instrumental in the mechanism of ozone depletion, have been observed from the station on August 1, 3, 6, 7, 8, 10, 13, 14, 15, September 3, 4, 21, 22, 26, 27 and 30. The display on August 10 was particularly vivid and that of September 30 showed classic development after sunset.

Data from the British Antarctic Survey (BAS) Rothera station (68-deg south, 68-deg west on Adelaide Island).

a) Ozone. Ozone measurements from Rothera are made using a SAOZ (Systeme d'Automatique Observations Zenithales) spectrometer. This is a research instrument, but the daily ozone values are available. These show a generally similar pattern of variation to that seen at Vernadsky, though day to day variation is a little less and minimum values are a little lower.

Rothera preliminary mean daily total ozone, (DU)
(0 indicates no data or data not available)

1997 August 1 - 1997 October 13

301 297 309 312 304 266 279 272 256 259

259 294 287 292 266 266 297 304 295 270 236

230 199 214 248 259 244 216 194 204 203

200 196 172 205 283 338 351 359 330 297

257 200 193 241 216 186 206 204 201 211

181 159 152 133 131 145 157 153 133 136

Running mean total ozone values fell from an estimated 350 DU in early July to 240 DU in early August. Since then the running mean has varied between 150 and 300 DU (55 - 10% depletion) under the influence of planetary waves with a period of around a month. Day to day variation is currently around 30 DU. Particularly low values were recorded on August 2^nd, when the station was affected by one of the ozone reduction events associated with the forming ozone hole, and on September 13^th and October 4^th and 11^th when the centre of the ozone hole passed near the station. Very high values near 370 DU were recorded on September 18^th when the circumpolar high ozone belt was over the station.

Vernadsky preliminary mean daily total ozone (DU).
Dobson No 31: Instrument constants revised 1997 October 7

1997 August 1 - 1997 October 11

255 257 275 285 285 254 239 237 235 248

236 298 291 296 258 287 314 312 305 300 253

237 200 205 255 254 251 232 213 211 208

200 184 153 205 269 355 369 371 371 286

268 213 185 253 249 217 244 261 263 241

225 197 174 149 150 160 200 181 158 168

TOVS satellite images from the US NCEP/NWS/NOAA Climate Prediction Center and EP/TOMS images from the US NASA/GSFC show the development of the ozone hole. The ozone "hole" is just past maximum extent and depth. It became more circular in shape around October 8^th, but then rapidly resumed its elliptical nature, extending over the tip of South America and the Falkland Islands between October 12 and 15. Minimum values at the centre of the hole lie around 120 DU, but ozone values are high over the continental edge at around 140-deg east. The normal circumpolar high ozone belt is present, with a very elongated high south of Australia and stretching into the South Pacific. UK Met Office analyses show that the polar vortex as an elongated 'S' shape, centred approximately on 75-deg south, 10-deg west, and aligned roughly 55-deg south, 50-deg west to 65-deg south, 80-deg east on October 16. The edge of the ozone hole passed over the tip of South America and the Falkland Islands on September 13/14 and October 12/15 and just clipped the area on September 23/24 and October 4/5.

Further information is available on the BAS ozone web page, which contains earlier bulletins, data, graphs and general ozone information. The url is:
http://www.nbs.ac.uk/public/icd/jds/ozone

Note that all ozone values in this bulletin are preliminary and are subject to revision from time to time when the instrument constants are re-evaluated. Final data will be archived with WOUDC, Toronto in due course, but preliminary data back to 1973 are available from BAS on request. All Dobson ozone data is reduced to the Bass-Paur scale as recommended by the WMO. If you use or pass on this data please make acknowledgement to J D Shanklin, British Antarctic Survey.